1. Field of the Invention
The present invention relates to an actuator, and particularly relates to an actuator that is installed in a digital camera, mobile phone, or other compact precision apparatus and drives a zoom lens.
2. Description of the Related Art
As a driving device for a lens unit of a digital camera, etc., an actuator that employs a piezoelectric element is used. For example, with an actuator of Japanese Patent No. 2633066, a driving shaft is affixed to one side of a piezoelectric element, and the other side of the piezoelectric element is fixed to a main device body. A lens barrel is slidably supported on the driving shaft, and the lens barrel is frictionally engaged with the driving shaft by making use of an urging force of a plate spring. Drive pulses of substantially sawtooth-like waveform are applied to the piezoelectric element, and the piezoelectric element deforms at different speeds in an extension direction and a contraction direction. For example, when the piezoelectric element gradually deforms, the lens barrel moves along with the driving shaft. Oppositely, when the piezoelectric element rapidly deforms, the lens barrel stays at the same position due to its mass inertia. Thus, by repeatedly applying drive pulses of substantially sawtooth-like waveform to the piezoelectric element, the lens barrel can be moved intermittently at a fine pitch.
However, with the actuator of Japanese Patent No. 2633066, because the moving distance, moving speed, and thrust of the driven member vary according to the position of the driven member and the operating environment, stable drive control cannot be performed.